High frequency measuring apparatus



March 7, 1933. J D WA LA 1,900,082

HIGH FREQUENCY MEASURING APPARATUS Filed March 15 1931 IN V EN TOR.

Jam w): 31% I J I I Wfl ATTORNEY Patented Mar. 7, 1933 I JAMES B. wALLAon, or wasnrne'ren, DISTRICT or COLUMBIA HIGH. Fnne cmior ran-est mate nrrnnarusf Application filed March l3,"1951. semi n; 522,437;

My invention relates broadly to high frequency signaling and more particularly to a inethodfand apparatus for determining the power output of radio transmitters and-de- 9 termining the efficiency thereof.

The object of my inv'entionis to provide an arrangement of apparatus for measuring radio frequency power in an antenna circuit at high frequencies and determining the plate circuit efficiency of high frequency amplifiers employed in signal transmitters.

The principles of my invention will be understood from the following specification by reference to the accompanying drawing which diagrammatically shows the apparatus of my invention.

Referring to the dra ing in detail, reference character 1 designates a chamber con 'taining an amplifier and its associatedpirs cuit 2; a thermostat 3; a heating resistor; and a fan 5 to establish air circulation within the compartment 1. The thermostat 3 by means of battery 6 operates the relay 7 which connects and disconnects the battery 8 from heater 4 in such manner as to keep compartment 1 at a constant temperature T f The watt meter 9 is connected so that the number of watts flowing into resistor 4 may be determined, when the heater is energized. The walls of compartment 1 are made of two substances, one to serve as a radio frequency shield and another to serve as a heatinsu lator. In the particular equipment used, the walls are composed of aluminum and pressboard. v I

Compartment 10 in the drawing contains a thermostat 11, a fan '12, a heating resistor 13 and a motorl l for driving both 5 and 12, thereby obtaining air circulation in both compartments 1 and 10. The thermostat 11 by means of batteryfi operates therre lay 15 which connects and disconnectsbattery-S from heater 13 in such manner as to ,5 keep compartment 10 at constant'temperature T However, to properlyfloperate' this measuring device, the temperatur-efof' T must be lower than T The walls-used for compartment 10 are made of celoteX' and 50 wood, however, any other heat insulating sheet material may be used. Nowsince compertinent 1 isma'iiitained atfalhigher'tmperature than "compartment 10,there will be a constant flow ofheat fromthe inner to the outer compartment. 'Instead ofmeasuri'ng this quantity of heat in calories per second,lit may be measured in terms of theaverag'e number of watts input required to keep compa'rtrn'ent 1 "at the proper temperature. The average power input may be 'determinedin this way; It is observed that power is applied to heater t only at intervals and not continuously because of the, action of the 'thermostat. From watt meter 9' determine the number of watts-flowing into heater l when the power is on; Next take two st'op' watches. Withcne stop watch measure the total time of certain number of periods of on. and off ofheater 4.1 During thi s 'sameperi'od,withthe other stop watch measure the length-of times that beaten-4 was v on7and add them to find the totaltimegon Nextdi'videthetotal time on by the total length of time of the selected number'of periods ofi and on, thereby obtaining 'the percentage of the time'that heater 4 stays on; Then multiply this percentage by the number of watts flowing when the heater is on, thereby determining the average power required to keep compartment '1 at the temperature T when compartment 10 is at T -Conipartment 16 contains a master oscillator circuit 25 for exciting the 1 amplifier 2 in compartment 1. Compartment 16 is enclosed in an aluminum box to prevent any feed-back fromthe antenna. The filament of the amplifier and master oscillator tubes 1 2 and 25 aresupplied rromgthe battery 17.

The plate supply for thema-stenoscillator 25 is supplied by battery 18." The'plate and V v loading coil of properiinductance the antenna circuit, sothat the entire circuit may be resonated atthe frequency at which transmission is desired. Under] this resonant condition, the antenna impedance is resistance 7 only and can be measured by any one of the V many methods already suggested for meas- T I torily only whenthe antenna is a non-reactive circuit will be worthless when the antenna circuit is reactive, as it usuallyjis under actual operating conditions at frequencies higher than 2000 kilocycles. Also it is diflicult to obtain: standards of radio'tfrequency resistanceto be incorporated within an antenna r values of voltage than the bias applied. The

' is true s measuring instrument which. are reliableat frequencies higher than 2000kilocycles, The method of my invention overcomes both of .thesedifliculties. r

A; measurement. of antenna power is taken in this manner. Apply properfilament volt agetothe amplifier 2, removingr plate voltage,wshield grid voltage,grid bias, and con-. trolfgrid'excitation, With the watt .meter 9 vand two stop watches, determinexas explained i hereinbefore the average power, supplied to heater 4 which isrequired to keep the inner thenormal filament voltage applied, This average power, input to resistor or heater-4; ,willlhereinafter-be referredto asaP pi Next. :apply'amplifier grid bias voltag'e, plate .voltrage, .shield, grid voltage, andfexcitation ap- ;plied' to the control grid. Thentunethe amplifierand antenna circuitto operate as. a transmitter;- The plate power to the amplifierm aybe determined by the voltmeter: and ammeter in-the plate circuit. Letithis power be -designatedias P p Now power l will be ,dissipatedin two ways; part of itzwillbe eX- pendedin heating'the plate of the amplifier andin amplifier plate circuit'losses, and the p v V In'the above expression P has already been determined, and P may be determinedfrom V The term P is the an tenna power which may be thereby deter mined. This deviceis veryzuseful for deter- V mining power output of, a transmitter qfor studying the effectiveness of various radicompartmentat-the proper temperature with other part in-the antenna 20.- Let the part expended-inside the inner compartment be I designated as P and the partexpendedin the antenna as Obviously, this equation source of power input to the inner compartmenth The ex'citation voltage appliedsto the control grid in most :cases,;has higher peak result is that thereis a rectified. component ofgrid current between the grid andithe 'filamenti Power'must be expended in moving the V electrons. from the amplifier filament to S I Poweris alsoapplied to'the shield grid'of Y the amplifien and all is expen'ded'in the form .of heat. Lettheshield grid power herein- "after be designated as P 1 It may. be determined "from the voltmeter and the ammeter inthe shieldjg'rid circuit; There is one other in heating the control grid of'the amplifier. V 1

The power expended in the gridcircui't of an amplifier is proportional to the v134th power of the rectified grid current; Let this power hereinafter be called equation holds true: 3

PG=KI1I34 v p I V a where [=rectified grid current v P Then this u tube, V I Since the co'nstant K hasbeen determined for a large number of tubes, and the current may be determined from'the rectified grid current instrument, the power P maybe readilycalculated, The temperature difi'erenc'e ofinner compartment above the outer compartment must be fixed sothat the powers P5, P and-P, V are not'enough' to hold the innercompa'rtment} 'i at its proper'temperature. Thenthe thermostat will provide a certain average power in- V. e [f -constantWhichdepends upon the put through resistor 4 to keep thetemperature constant. This power supplied through resistor 4 under the control-conditions speci fied will be called and maybe determined by the watt meter 9 and the two step: watches as explained hereinbefore Now, since the 7 average power input from all sources to the inner compartment is-the same at all times,

nerze All terms on the right hand side may" be measured or calculated, andtherefore P the plate power expended in the inner compartiment may be evaluated. Now Equation "(1) rearranged may bewritten in this manner:

' P;,=P %P instrument readings.

ating devices, for determininglthe efliciency V p of various types of plate circuits, for detervother factors affecting the efiiciency of a radio transmitter, I V

If theeflective resistance of the antenna at any point is required, it may be found by dividingthe. radio frequency power by the square of, the current at that point The;

by the plate input -power.;

overall plate efliciency'of any amplifiermay r be determinedby dividing theantenna power There are two other ways: tlie I dei Oh i vice may be used. The thermostat maybe eliminated from the inner compartment and the temperature rise of the inner I compartment for a given power input may be measured. Then a Calibration curve might be drawn therefrom. When the amplifier is in operation. the temperature rise might be 'noted and the losses determined therefrom.

The device might also be used in this manner: The thermostat may be eliminated, and a'steady power put through resistora, the

amplifier being off Note the temperature of the inner compartment under this'condition. Next put the amplifier on and reduce the steady power input'to resistor 4 until the inner compartment has the same noted temperature. These two methods are not to be preferred to'the method I'have described previously.

The general method'of measurement set" forth herein is useful in measuring the losses in any device, provided all losses appear as heat or in any form which can not escape from the inner compartment. Any desired device may be substituted for the amplifier. in the inner compartment and by illustrat-' ing my invention in connection with an ampllfier I do not intend that any limitatlons shall be imposed upon my invention.

I have found the measuring apparatus of my invention highly accurate in the measure ment of high frequency power. The system 1. The method of measuring. power .in a

reactive antenna circuit whicheonsists in op erating a power amplifier into the antenna circuit, determining the power required to maintain the parts of the power amplifier at constant operating temperature, measuring the heat loss and determining therefrom the power transferred from said amplifier to the antenna circuit. p

2. The method of measuring power in 'a reactive antenna circuit which consists in op erating a power amplifier into the antenna circuit, determining the average platepower and the power disslpated 1n losses n the plate circuit of the power amphfier and other losses in said amplifier as represented by'dissipated heat and determining therefrom the power transferred by said amplifier, to sair antenna circuit. 7 i

3. The method of measuring power in a reactive antenna circuit which consists in op- 5. The method of erating a power amplifierinto the antenna circuit and determining the value of plate power and the value of power dissipated in heating the plate and the plate circuit losses,

determiningthe other losses in said amplifier, and subtracting the value representing all of said losses from the first mentionedvalue to determine the power delivered to the antenna circuit by .said amplifier.

4. The method of measuring power in a reactive antenna circuit which consists in operating a power amplifier into the antenna circuit, measuring the plate power of the amplifier, determining the value of the total;

power dissipated in heating the plate and the power dissipated in plate circuit lossesdetermining the other losses in said amplifier and solving the following equation:

where 1? equals the plate power consumed by the amplifier and P equals thepower dissipatedin heating the plate the plate cir-. 'cuit losses and the other losses in theampli-' fier for thus determining the power transferred to said antenna circuit from said amplifier. I

a high frequency antenna circuit which consists in operating a power amplifier into the antenna circuit, determining the value of plate power consumed by the power amply tier and thermally determining the value of the power dissipatedin heating the plate,

the plate circuit losses andthe other losses in the amplifier and subtracting the total sum representing second value fromfthe first value measuring the power in for determining the power transferred from said amplifier to said antenna circuit. v

6. A method of measuring thc'power in an antenna circuit athigh frequency which consists in operating a power amplifier into an antenna circuit, enclosing the power amplifier within a temperature controlled cabinet,

maintaining the amplifier at constant operating temperature, measuring the total power dissipated in heat by said amplifier under operating conditions, and determining the high frequency power in the antenna circuit by su tracting the integrated value of the power dissipated in'heating the plate, the

plate circuit losses and other losses fromthe value of plate power.

7., In an apparatus quency load circuit, a plurality of nested com.- partments, a power ampl fier disposed in a centralcompartment and connected with said highfrequencyload circuit, means for establishin convection air currents withm each of the compartments, heating means in each compartment, thermostats in each compartment for controlling the operation of the heating means therein, and means for determining the amount of thermalenergytransfor measuring high frev quency power in electrical circuits, a high fre-o zferred a between said compartments for. de-

' terniiningthepower transferred from said power, amplifier to said load circuit. I 8; In an apparatus for measuring power 1-11 hi glrfrequency circuits, a. l radio'yfrequency *load circuit, a power amplifier circuit-for del vering radio frequency 'powerito sa1d radio frequency. load circuit, a pairof enclosing chambers,'said power amplifier disposed centrally-within one of said chambera'means for intermittently heating each of said chain ebers, thermostats 111 each of said chambers --for controlling said means, means for operating sa-id ainpiifierinto said radio frequency loads-V circuit, and nieans for measuring the heat transferred between saidchambers for V determining :the power transferred to said radio-frequencyloadfcircuit; P

r 9; In an apparatus for measuring radio frequency "circuits, the combination with a: high frequency. transmission circuit pair of. enclosing chamb'ers,-,a power amplifier disposed within one of sa d chamberss'and connected with-said radio frequency transmission circu t, means for heating each i oflsaid chainbers, thermostats in each offsaid chambers for controlling? the operation of said heating means and maintaining constant the respective temperaturespf; each of said chambers, means in oneof said'chambers for. circulating the air within eacho-f'said'; cham- "bars, and means' for ,ineasiiring the heat energy-dissipated insaid chamber containf in g. said power A amplifier from' sources other than-said means foriheatin g-said' power 10; Inv an apparatus for. measuring power *iii a radio frequencycircuit, the combination with'a high frequency transmission circhambers for controlling-the, operation; of

said heating *ineans, said thermostats operating to maintain said chambers at different temperatures and means for -measuring the transfer ofrheat from one chamber to another during the operation of .s'aid amplifier for 1 'Cleiielflllillp the power transferred to said ""if' l uenc"'ouit "cow 7. s lad O f eq y 9 7 r 3 p er in a high frequency c1rcu1t,a high'frequen'cy V amplifier. v 7

- 'l'l-i In an apparatusfor measuring power in'radio frequency circuits, the combinat on with a high frequencytransmission circuit fa pair of enclo'singchambers, the one sup 7 rounding the other, a power amplifier dis-, posed within the nner said chambers and con- "iiecte'dwith said radio-frequency transmiss on circuit; means for heating each of said chain,-

' bers, thermostatsin eachof said chambers for V controllingtheoperation-of said heating, meansuand ma ntaining constant the respective, temperatures of each, of saidlch'ambers,

power in said thermostats op crating to maintain the outer chamber at alowertempera'ture than the innercchambenand means for measuring the heat 'energydissipa-ted ii said' chamber 1 containing said power amplifier from sources, other: thanlsaid means for heating said power I circuit, a pair of-nestedchambers, a power amplifier disposed 111 the inner chamber,

means for intermittently heating each of said chambers,:means for maintaining the temperatureiwithin each of said-chambers c011 stant and; atpredetermined,:dift'erent value means for operating saidpower'amplifierinto said high frequency current consuming circuit, and means for determining the "Va-11 17 of power dissipated in the transfer ofthermal 7 energy between; said inner and outer; cham bers while maintaining said power amplifier at a uniformoperatingtemperature.

' 13. In an apparatus for measuring power consumed in a high frequency circuit, a pair "of spacially-related inner and outer compa-rt ments, apower amplifierdisposed in the inner compartment, means for maintainingleach of said compartments at different predetermined fi edtemperatur-es, means-for operating said power amplifier into saidhigh frequency circuit, and means; for'measuring the thermal energy transferred'fromsaid inner to said outer compartment under operating conditions of saidpower'= amplifier for determining fier to said high frequencycircuitk firepower-transferred fromsaid power ampli- V :14. i In an apparatus for measuring-power consumed in a higlrfr'equency circuit,a pair of spacially related inner and router compart- I ments, a'power amplifier disposedlin 'theinner compartment, means for maintaining said, 7

inner compartment at a selected constanttemperature, means for maintaining said outer compartment at a lower constant tempera-V ture, means for operatingsa'id power ampli 'fierinto said high frequency circuit, and means for measuring the power dissipated I by the transfer of heat from I said innerto said outer compartments. v

15. In an apparatus forineasuring power load circuit, a pair of chambers the one sur- I rounding the other, a power tube amplifier having cathode, grid andplate electrodes disk posed in the inner chamber. and havingits outputconnected to 'saidload circuit, inde- I said I chambers for controlling the operation of each of'said last mentioned heating means for maintaining said chambers'respectiyely at constant temperatures, said-innerchamber being maintained at higher a temperature a than said outer chamber, means for measuring the average power input to said heating means in said inner-compartment undei' different load conditions, and means for determining the electrical energy dissipated by the grid and plate electrodes of said power amplifier. 7

JAMES D. WALLACE. 

